Re: paraffin sections turning white

From:

Mary North

In my experience, this happened when the trimmed block face was not
rehydrated sufficiently on tissue that was over-dehydrated in the processing
schedule. It was more prevalent in small biopsies which tend to get
overprocessed. A cotton ball or Kimwipe soaked with warm water
and held onto the block face will rehydrate better than the cold ice cube
or water. A pad soaked with a dilute solution of Tween 20 held on the
block face will rehydrate even better, if necessary, but take care not to
oversoak the face or the tissue becomes too soft to section.

I've been having trouble lately with the tissue
portion of my paraffin sections turning white (either in patches or the entire
tissue) and appearing really dry, even cracked. The paraffin surrounding
the tissue does not change appearance. This type of tissue normally
doesn't turn white.

The sections come off the microtome easily and are
smooth, and when I first pick them up off of the water, they look fine.
But, after about 10 minutes or so, they start turning white. The
appearance varies some from section to section, and a few don't ever turn
white. I hope I've described this well enough.

An expert has told
me that it is probably the processing, but I'm concerned because we have
received blocks from many different sources. This continues to happen with
each block, and wasn't happening a year ago. Has anyone experienced this
problem before? Does anybody have any ideas as to what I could be doing
wrong? Thanks.